For anyone interested in the manufacture of guns in America, as per the 1880 census (Duh! who here isn't!), the Charles Finch 1882 report is essential reading. Finch was commissioned by the government to do an overview of gunmaking in America coincidental with the census. The eBay offering is a reprint:
#360088988417 "Manufacture of Fire-arms and Ammunition 1882."
Finch details the Interchangable System of gun mamufacture that Parker Bro's pioneered for shotguns and finally announced in the May 1877 catalog. I have no interest in this book, and don't know the seller, but it proved so valuable when I wrote several chapters of my new book that I thought someone on this Forum ought to share the wealth of info. EDM